Japanese e-commerce giant Rakuten has confirmed it is leading a $100 million investment in Pinterest, together with existing backers Andreessen Horowitz, Bessemer Venture Partners and FirstMark Capital plus angels.

WSJ reports sources as saying the deal means a $1.5 billion valuation.

Rakuten CEO Hiroshi Mikitani (via announcement):

“While some may see e-commerce as a straightforward vending machine-like experience, we believe it is a living process where both retailers and consumers can communicate, discover, and curate to make the experience more entertaining.

“We see tremendous synergies between Pinterest’s vision and Rakuten’s model for e-commerce. Rakuten looks forward to introducing Pinterest to the Japanese market as well as other markets around the world.”

In other words, Rakuten is excited about how enthusiastically Pinterest users clip and share items they might want to buy.

Pinterest CEO Ben Silberman:

“Our goal is to help people discover things they love, by connecting people through their shared interests. Bringing Rakuten on board gives us an amazing opportunity to move a step closer to this goal.”

Pinterest’s visual presentation of those products is not the only potential boon to e-tailers (it wouldn’t take a rocket scientist to present product listings in this way); the tie-in with social sharing could effectively enable social commerce.

There is a wide number of retailers for which Pinterest could perform this role:

• Rakuten has built up its heft through acquiring the online retailers Buy.com in the U.S., Priceminister in France, Ikeda in Brazil, Tradoria in Germany and, recently, Play.com in the UK.
• It also recently bought the Kobo e-reader and e-book store business.
• And it has made investments in Russia’s Ozon.ru and the AHA Life luxury shopping site.

Pinterest has boosted web referrals for sites in certain categories like women’s lifestyle publishing, so some publishers, as well as retailers, had become excited about the possibilities.

It’s unclear what the e-commerce investment means for the media’s current Pinterest penchant, but some pundits think content and commerce is a marriage made in heaven.

The Next Web had reported on Wednesday its expectation that Pinterest would announce a funding round at a $1 billion valuation on Friday, which is also Facebook’s IPO day.

Pinterest had previously taken a total $37.5 million from angels, Bessemer, Ron Conway, FirstMark, Andreeson Horrowtiz and others, through an angel and two proper rounds.